12AX7 / 7025 Tube Reviews

(View our complete selection of 12AX7 vacuum tubes)

12AX7 Tubes on guitar strings Review Notes - how we conducted the review

What makes a good tube? - detailed description of the test parameters

Tube comparison table - reviews at a glance
Full reviews of the tubes we tested (click to go to its review):
Northern Electric 12AX7
Preferred Series 7025 / 12AX7
Mullard CV4004 / 12AX7 (reissue)
Mullard 12AX7 (reissue)
Gold Lion ECC83 / B759
Svetlana 12AX7
Tung-Sol 12AX7 (reissue)
Electro-Harmonix 12AX7-EH
Sovtek 12AX7-WA, 12AX7-WB
Sovtek 12AX7-LPS
Sovtek 5751
JAN-Philips 12AX7WA
JAN-GE 5751
JAN-Philips 5751
JJ / Tesla ECC83-S / 12AX7
Ei 12AX7 / ECC83

12AX7 Audio Vacuum Tubes Top Sellers

Review Notes

Guitar Amp Tube Reviews written by John Templeton.
The tubes used in this review were selected at random from thetubestore.com's inventory of untested tubes. For each tube used in the test, two were taken since there was no pre-screening involved. The aim was to get a sample that would be practical to work with but allow for variations in the tubes or prevent picking the only dud in a lot.

The test amplifiers used were very different. One was a 100-watt Trace Elliot Speed King with 4 x 12 cabinet, and the other was a Fender Blues Junior combo amp. This allows the high power, high gain crowd and the more conservative players to get the fairest evaluation possible. Some tubes were clearly better suited in one application or usable in both. All tubes were used at the input amplifier stage of the amp since this seems to be where most people develop their perceptions of how good a pre-amp tube is.
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What Makes A Good Tube?

The musical detail or ability to reproduce the sound of the instrument is a key factor in assessing a tube for guitar amplifiers. There is no perfect tube available. Each one has strengths, weaknesses and certain factors that contribute to its overall ratings. Usually a compromise is arrived at in the search for premium tone.

All tubes will exhibit some degree of microphonics. Microphonics do not mean that a tube is unusable. You just have to screen them a little closer and determine where they are best suited for use. Input pre-amps are the most sensitive areas of the amplifier. When used in this application most tubes will generate some noise if you tap on them with a pencil during operation. Keep in mind that doing so can actually damage the tube and make it more microphonic or cause it to fail if you hit it real hard. Although they are screened prior to shipment a tube is an electromechanical device and can be damaged during shipment. A microphonic tube will ring, howl or produce general feedback problems. It will be more noticeable at louder volumes or when used in close proximity to a speaker, typically in combo amps. If the tube has good tone at lower volumes and is free from unwanted noise, you use it in a less sensitive part of the circuit, such as tone recovery or phase inverter applications.

Noise is more of a problem than microphonics. A noisy tube will make random popping noises, crackle occasionally or just hum. All tubes have a certain noise floor; this is the inherent background noise that the tube makes in operation. Typically, you will notice this as a soft hiss or "white noise". Tubes designed for high gain can exhibit more background noise. Other components can cause noise problems that may be blamed on a bad tube. Plate resistors are notorious for causing hiss and crackling as they age and begin to fail. A new tube may better amplify these defects, so try substituting another new tube to be sure of the source of the noise.
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12AX7 Audio Vacuum Tubes Comparison Chart
Click to view our 12AX7 / ECC83 / 7025 Tube Comparison Chart

The Complete Reviews

NE-12AX7 Tube ThumbnailNorthern Electric 12AX7 - It’s not often that something truly special comes along. The Northern Electric 12AX7 is brand new and exclusive to thetubestore. This is not something that came along overnight. We have been developing and testing this product for almost 2 years to ensure that you will be buying a product that stands up against anything on the market, new or old. To do this we have traveled to the manufacturer to observe production and quality control methods, and obtain pre-release samples that have been in the field for over a year now. Our hard work and close relationship with the manufacturer have paid off.

Samples have been tested in our audio reference equipment and in the amplifiers of working musicians that have logged many hours and many miles. It’s the feedback from these testers that tell the tale. No failures of any kind have occurred under the most demanding conditions and, in round table discussions and blind testing in the studio, players consistently preferred the Northern Electric over any pre-amp tube we currently offer.

The Northern Electric 12AX7 is made with the highest quality materials. From the glass bottle to the gold plated pins, everything is designed to give you unsurpassed audio quality. This tube has very large smooth plates. This design is much like a Telefunken smooth plate but a bit shorter. This design provides plenty of gain while maintaining an extremely low noise floor. Like any large plate tube, tapping on the bottle with the volume turned up will generate some mechanical noise, but the Northern Electric is not in any way prone to microphonics. It has been torture tested in a JTM 45, a Deluxe Reverb, an Orange 50 watt combo and Bandmaster Reverb, with no failures or noise problems after hundreds of hours in clubs or in the studio. It doesn’t matter if you use an American or British design, this tube works.

In our listening tests it was easy to hear that the tube did not change the voice of the amplifier as some pre-amps do. The Northern Electric enhances the sound across the entire spectrum. Our testers have reported no noticeable spikes or weakness in the lows, mids, or high end. The highs are very smooth with a balanced midrange response and warm, full bottom end. If you notice any frequency anomalies you should have a look at your speaker of choice as that is likely where the problem is. As you drive your guitar amp harder you will notice that this tube is passing both the fundamental note and beautiful spectrum of harmonics to the power amp. The resulting overdriven signal is warm and complex but never gets confused or mushy sounding. It is absolutely the best 12AX7 that we can offer you.

At $59.95 it is not cheap, but if you want uncompromised tone this is the one for you.

Preferred Series 7025 12AX7 Thumbnail ImagePreferred Series 7025 / 12AX7 - A great sounding 12AX7 tube type that reminds me a little more of the ECC83 that EI made in the old days. That's a pretty nice compliment. I compared this tube against an old EI and Telefunken smooth plate and there was very little difference. Lots of gain with a rather low noise floor. No microphonics issues at all. Very good considering the large plate size. Spot welding may be better for microphonics than crimped plates. I tried it in all the standard guitar amp duties and it was fine. Fabulous in Blackface Fender amps. We tried this 7025 in a 66 Vibrolux reverb 2x10 combo and the tones were all there. Light and shimmering or really aggressive, it's all good.
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TS-12AX7 Audio Vacuum Tube ThumbnailTung-Sol 12AX7 - There are only so many ways to describe tube tone and most have become cliches. The Tung-Sol 12AX7 has the gain and drive of a Chinese 12AX7 and the pure tone of a Mullard or Brimar from the U.K. I've had two people come to me recently with amps they thought were in need of complete overhauls. In both cases, careful examination revealed no serious problems and all the tubes "tested" as good. At the end of the day, I replaced the NOS Mullard and RCA pre-amps (one in each amp) with a reissue Tung-Sol 12AX7. In both cases the owners were very impressed and thought that their amps had been restored to full health. Believe it or Not.
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GL-ECC83 12AX7 Audio Vacuum Tube (Premium) ThumbnailGold Lion ECC83 / B759 - Yet another great tube from Russia and another in the line of large plate dual triodes. By my count we have the Sovtek 5751, Sovtek 12AX7 LPS, Mullard and now the Gold Lion brand. A quick glance and you might think they were all the same but careful inspection reveals physical differences in construction and plate coatings. Listening to these tubes reveals even greater differences.

It is very smooth and pleasing to the ear. I attribute this to the broad midrange response. In audio or guitar equipment, grating highs and booming lows will give you listening fatigue or make you think your amp just sucks. The Gold Lion's voicing is such that the midrange response seems full, while the highs and lows are nicely controlled. This tube would be great if you are retubing one of those classic old radio consoles. It would also be great in a Marshall JCM800 series amp to tame the bright channel and cut some of the crazy high end.

The best news with the Gold Lion ECC83/B759 is that I could not get one to feed back at major sound pressure levels in a combo guitar amp. Finally.

This tube in your first gain stage will deliver a most pleasant reproduction of your audio source or make your guitar amp sound warm with real creamy drive when pushed with hotter pickups.

NOTE: For those of you that love to take a pencil and whack hot tubes, you will be rewarded with a satisfying, loud, "PING". It's the nature of the beast with any large plate dual triode used in V1. If you get uncontrolled squealing at higher volume levels or if touching the amp causes a ringing noise you probably have a genuine microphonics problem. If you like to tap your tubes all the time to see if they are microphonic, you will likely cause a genuine microphonics problem.
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MU-CV4004-12AX7 Mullard Audio Vacuum TubeMullard CV4004 / 12AX7 Reissue - This tube looks nothing like Mullard tubes of old but it has a lot to offer. This is a small plate design more suited to high gain amps. Old Mullard with large plate structures are sought after for audio systems because of their gain and detail. Those same attributes are the last thing you want in your Marshall stack.

The smaller plate reduces noise. They are dead quiet both electrically and mechanically. Nice thick bottles and well aligned internals also help. If you currently like the Tungsol 12AX7 you will love this tube. The gain is similar but overall it is quieter and a bit warmer to my ears.
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MU-12AX7 Audio Vacuum Tube ThumbnailMullard 12AX7 / ECC83 Reissue - This is a nice tube but in my opinion better suited to home audio than guitar amps. The tubes have well balanced triode pairs and a very even flat response. Compared to a Tung Sol it sounds a bit flat, but so does a NOS Mullard. Microphonics is not an issue despite the larger that average plate structure. The transconductance on my sample was the same as two NOS samples I measured. Not really high gain at all, but a real good noise floor and a nice smooth tone that doesn't encourage ear fatigue the way some preamps can be. The Tung-Sol 12AX7 is my favorite preamp for guitars because it accentuates highs and lows. The Mullard adds virtually no tone coloring and is smoother sounding to my ear than a JJ ECC83S. For hi-fi gear the Mullard will likely be a winner but there are better choices for guitar amps for less money.
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EH-12AX7 Audio Vacuum Tube ThumbnailElectro-Harmonix 12AX7 - These are not relabelled Sovtek 12AX7-LPS tubes. There is a marked difference in construction and performance. The 12AX7 EH has a nice balanced sound, fairly low noise floor and excellent performance in terms of microphonics. The lack of microphonics may be in part from the return of the shorter plate structure or materials.
I've had some samples that were tried in various amp stages. Pre-amps, tone stacks and phase inverters, a winner in every location, although I like to use a 12AT7 for reverb circuit drivers due to their lower gain rating (just a personal preference of mine).
I have used the EH to successfully tame amps that defied all other attempts to kill microphonics and unwanted feedback. This tube is a winner, buy 'em and try 'em, they may be just the piece you've been looking for.
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SOV-12AX7WA and SOV-12AX7WB Audio Vacuum Tube ThumbnailSovtek 12AX7-WA, 12AX7-WB - I've grouped these two together because they have essentially the same sound. The only noticeable difference between the two was a bit more gain from the WB model. These tubes are rugged little brutes, and that's probably why they are OEM components for many major amp makers. Both tubes could be whacked with a stick at full volume and not show much in the way of microphonics - but DON'T DO THIS AT HOME, as it is often a destructive test for tubes. They don't have the best sound in this type, being prone to the occasional pop or tick. The sound quality lacked any real character but was acceptable. If the budget is tight, their affordability will be attractive. Also, keep in mind that many amp designers design the equipment to sound best with the tubes they will use in production. I have a friend that claims his amp only sounds right using Chinese pre-amp tubes, but your mileage may vary on this issue. If you like the Sovteks then go for it, particularly if you will use them in high gain applications with lots of effects.
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SOV-12AX7LPS Audio Vacuum Tube ThumbnailSovtek 12AX7-LPS - This is an entirely new design from Sovtek and a great step up in sound quality. They have very large ribbed plates and great sound reproduction. I found them very smooth and well balanced in terms of bass, mids and treble response. The large plates make them more prone to microphonics and in combo amps, so they can be a problem if you like to run things wide open. It is still the best thing Sovtek has produced in a 12AX7, with very good gain and low noise. I would advise against using them in compact high-powered combo amps where they will be subjected to lots of vibration. One other note about the construction of these tubes is they have filaments that are almost completely encased in the plate structure. They often don't "light up" when working properly. This is not a problem, it's normal for the LPS.
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GE-5751 Audio Vacuum Tube Thumbnail JAN-GE 5751 - While not really a 12AX7, it shares the same pin-out arrangement and is designed for less gain in favor of lower noise and microphonics. It worked well in both test amps and can be used to advantage if your amp has too much grind. One of these should calm things down a bit. The 5751 is an affordable alternative to the 12AY7 used in original Fender tweed amps and can be subbed for a 12AT7 like a reverb driver tube. In this application, you will get good gain with a warmer sound than the 12AT7. The even balancing makes them a nice phase inverter and allows you push the front end of the amp a little harder.
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SOV-5751 Audio Vacuum Tube ThumbnailSovtek 5751 - The Sovtek 5751 is an affordable alternative to the 12AY7 used in original Fender tweed amps and can be subbed for a 12AT7 reverb driver tube. In this application, you will get good gain with a warmer sound than the 12AT7. The even balancing makes them a nice phase inverter and allows you push the front end of the amp a little harder. If you wish to use a 5751 in a 12AX7 position to reduce gain we recommend you use the JAN-Philips 5751 tube.
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JAN-Philips 12AX7WA - If you really want NOS (New Old Stock) tubes, this is one of the best buys out there. The Philips tube is well built and should be long lasting. The tubes I tested had lots of gain while still maintaining very good noise levels and good tolerance for microphonics. The tone was solid in the midrange with very wide dynamic response. If you're not careful with your setup, you can get these tubes to be boomy in the bottom end and shrill in the high end. I found that they were great with the tone controls set flat. Great in both combo amps and monster stacks.
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JAN-Philips 5751 - Now here's a surprise, and a good one at that. The 5751 is typically referred to as the lower gain 12AX7. The fact is they are just dual triodes with the same pin-out as others in the 12AX7 family. This particular batch of NOS 5751 fails to perform as most 5751 tubes. It's not lower gain, it's not darker. These JAN-Philips 5751 tubes are one of the best dual triode tubes I've ever heard. They have nearly 12AX7 gain, extremely low noise, and frequency response that covers any audio application. They sound good in everything I've tried them in but particularly shine in single ended, simple amp circuits. Good examples would be a Fender Champ, tweed Princeton, Gibson GA-5 or any amp that has a preamp, power tube and rectifier. One of the best deals available in an NOS 12AX7, is actually a 5751!
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NSV-12AX7 Audio Vacuum Tube ThumbnailSvetlana 12AX7 - For several years the original Svetlana 12AX7 tube from St. Petersburg (Winged "C"/SED) tried to develop a good 12AX7 and mostly failed. The current production Svetlana is a New Sensor product and is a member of 12AX7-EH and Tung-Sol 12AX7 family. All three of these tubes is virtually identical. The biggest difference seems to be in plate coating, gain and sound quality. I find the tube to sound a bit smoother than the EH and it has less gain than the Tung Sol. If you are not inspired by the Electro Harmonix and also find the Tungsol too grainy then this is the tube you want to give a chance. It has everything you want in a good pre-amp. Low noise, no Microphonics issues and very clear and open without being too bright. The construction is on par with the more expensive Tungsol. The price point on this 12AX7 tube is great because it will hold its own with more expensive options. Samples seem very reliable. If you like the JJ ECC83S but want something with a litter more glimmer this is where you should put your money.
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JJ-12AX7 Audio Vacuum Tube ThumbnailJJ ECC83-S / 12AX7 - This tube sports a different plate design than found in most 12AX7's. When you look at them you can't help but think that they must be rugged and good for the musician on the road. The compact plate structure does nothing to dampen their sound or dynamic response. I find them to be well balanced. While not as harmonically rich as others I tested, they do provide high gain without the usual noise and microphonic problems you would expect. This is great sound for your dollar. If you're using a combo amp and find the Philips a little rich sounding, the JJ ECC83 may be your solution.
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Ei 12AX7 - This tube should win an award for best and worst in class. The first one I tried squealed in the combo amp and produced a ringing sound in the half-stack. (Remember these were not from the pre-screened tubes that thetubestore.com sells.) The second one I tried was fantastic. There were no microphonics problems with this second tube. The scores for microphonics (2 and 4) are for each individual tube that was tested. A few phone calls to another tech confirmed my suspicion: there is a high failure rate when initially screening these tubes for microphonics. The ones that do pass testing are wonderful; they are very musical sounding with lots of gain and a very low noise floor. When playing the guitar you could really get the benefit of their dynamic range. They can reproduce soft passages accentuated with a sharp punch and you don't have to go near the volume controls. I'm keeping the test tube for some long term testing. These would be great tubes for home audio applications. Due to the microphonics problem, I'm unsure as to their roadworthiness. At home or in the studio, they will deliver great results. The only caveats are; make sure they are carefully screened and don't think about using them in high gain combo's unless they are tested in a similar amp first.
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